If you’re old enough, you may remember a time, maybe back in your childhood, when someone measured your intelligence and assigned a number to it. I suspect that you have been either proud of that “IQ,” or perhaps a little bit chagrined about it, from that day to this. The general belief back then was that intelligence was a genetic endowment, along with eye color or a propensity for baldness.
We now know this is simply not true. Your brain — every brain — is a work in progress. It is “plastic.” From the day we’re born to the day we die, it continuously revises and remodels, improving or slowly declining, as a function of how we use it. If a brain is exercised properly, anyone can grow intelligence, at any age, and potentially by a lot. Or you can just let your brain idle — and watch it slowly, inexorably, go to seed like a sedentary body.